PODOSPHAERA. 



175 



This mildew has inflicted great 

 Dusting the threatened 



P. myrtillina Schub. on leaves of Vaccinium MyrtUlus (bil- 

 berry), V. uliginosum, and JSmpetntm nigmm (crowberry), (U.S. 

 America). 



Erysiphe. 



The perithecia contain several asci, each with two to eight 

 oval hyaline spores. The appendages are like these of Sphae- 

 rotheca, simple and thread-like. 



Erysiphe graminis D. C. Mould or mildew of grass and 

 wheat. Grass and cereals, especially wheat, often suffer serious 

 damage from this parasite. The mycelium appears on the leaves 

 as white or brownish spots, generally on the upper surface. 

 Colourless conidia (Oidium. vionilioides, Lk.) are produced acro- 

 petally in chains. The somewhat rare perithecia have brown 

 appendages, and contain eight to sixteen asci, with four to 

 eight spores each ; the spores mature in spring as the dead 

 leaves lie on the ground. 

 loss both in Europe and America, 

 crop with " flowers of sulphur " will 

 probably check the first stages of an 

 attack, but care in destroying infected 

 crops is by far the most effective 

 preventive. 



Erysiphe martii Lev. This fre- 

 quents various Leguminosae (clover, 

 beans, vetches, peas, lupines, etc.), 

 Cruciferae, and other plants (Britain 

 and U.S. America). 



Er. umbelliferarum De Bary. 

 Occurs on various Umbelliferae 

 (Britain). 



Er. communis Wallr. on tobacco, also on various Eanun- 

 culaceae, Papilionaceae, etc. (Britain and U.S. America). 



Er. tortilis Wallr. on Gornus sanguinea (Britain and U.S. 

 America). 



Er. galeopsidis D. C. on Labiatae (Britain and U.S. 

 America). 



Er. cichoriacearum D. 0. on Compositae, Boragineae, and 

 also causing considerable damage to cucumbers (Britain and 

 U.S. America). 



Fig. 72. — Erynphe umbeUiferarum. 

 Germination of a conidium (sp) on 

 Antki-iscus sylvestris. An attach- 

 ment-disc has been formed, and a 

 ECerm-tube has penetrated the epider- 

 mis to become the first haiistorium. 

 (After De Bary.) 



